The structure of a wellbore of an oil or gas well generally consists of an outer production casing and an inner production tubing installed inside the production casing. The production tubing extends from the surface to the required depth in the wellbore for production of the oil or gas. Various tools such as plugs, chokes, safety valves, check valves, etc. can be placed in landing nipples in the production tubing to allow for different production operations or the downhole control of fluid flow. Also, tools like bridge plugs, packers and flow control equipment are placed in the production casing to control production or stimulation operations. Force generating tools are needed both to exert a pushing force to set the tools in the landing nipples and to provide a pulling force to retrieve the tools. It is preferable to have the force generating tools pressure balanced so that the same force may be applied both in pulling and in pushing operations, irrespective of the pressure in the wellbore.
A downhole force generator is disclosed in U.S. Pat. No. 6,199,628. A downhole force generator is disclosed in U.S. Pat. No. 5,070,941. A locator and setting tool is disclosed in Canadian Patent No. 2,170,711. These 3 patents describe virtually the same technology, in different variations. None of these prior art tools are pressure balanced to provide equal force in pulling and pushing operations. As detailed in the article published by Halliburton Energy Services in the June 1996 edition of the SPE Drilling & Completion magazine, “Any pressure differential increases the available force with the DPU in tension and decreases the setting force in the extension mode. This is because (1) the DPU is sealed to the well pressure through redundant sealing elements maintaining internal parts at near-atmospheric pressure, and (2) the well pressure acts on the power rod's sealed diameter.” This is a disadvantage, especially in high-pressure wells. A high enough downhole pressure will render these tools unusable. Additionally, none of these tools provide a simple mechanical tool, particularly for the retrieval of downhole tools.